I am grateful to all the people who contributed to the completion of this dissertation either by continuing the work detailed in it or by providing support during the process. Many of the experiments described in this thesis were carried out in various national laboratories.
Intramolecular Conflict
The conformation of a polymer in solution depends on the molecular architecture (substituents of the polymer chain, length and topology) and interactions with the environment (the solvent, other polymer chains and external fields). However, it is assumed that the reader is familiar with many of the concepts and techniques of polymer physics.
Polymer Chains in Solution
A more sophisticated model for a polymer is the free-rotating chain (Figure 1.3), in which the angle θ between adjacent segments is fixed at a given value (e.g. the carbon-carbon bond angle of 109°) . In a "poor solvent" polymer-solvent interactions are significantly less favorable than polymer self-interactions and solubility is limited.
Experimental Characterization of Polymers
The location of the transition between the two behaviors and the slope of the plateau can be used to determine the Rg of the polymer coil. The ratio between the two characteristic radii (Rg/Rh) can be used to study the compactness of a particle.
![Figure 1.6: Scattering function of a polymer coil. This was calculated using the polymer excluded volume scattering function[14] in the IGOR Pro macros written by Steven Kline[15]](https://thumb-ap.123doks.com/thumbv2/123dok/10408655.0/28.918.224.733.116.435/figure-scattering-function-polymer-calculated-excluded-scattering-function.webp)
Architecturally Complex Macromolecules
- Bottlebrush Polymers (Chapters 2 and 3)
- Side-Group Liquid Crystalline Polymers in Liquid Crystalline Solvent (Chapter 4)
- Complementary Associating Polymers for Mist Control Kerosene (Chapter 5) Complementary associating polymers have long linear backbones with associative
- Theoretical Study of Membrane Particle Interaction (Appendix A)
The competition between the conformational freedom of the side chains and the backbone is resolved by a conformational compromise. The conformation of a bottlebrush polymer in solution is largely determined by the length and chemical composition of the side chains (as long as the backbone is longer than the side chains with a cylindrical rather than spherical composition).
Introduction
The length and polydispersity of the side chains are well defined and precisely matched for a series of bottle brushes with different backbone lengths grown from a given series of macromonomer. When the backbone length (Nb) is less than or equal to Ns, the molecule resembles a star polymer (with spherical symmetry)[47].
Experimental .1 Materials
- Characterization Methods
- Synthesis of Alkyne terminated Norbornene
- Typical ATRP procedure for tert-butyl acrylate, styrene, and deuterated styrene
- Conversion of Terminal Bromine to Azide
- Click coupling of azido terminated polymer to norbornene-alkyne
- Purification of Macromonomers
- ROMP of Macromonomers
- Hydrolysis of poly(tert-butyl acrylate) into poly(acrylic acid)
- Making bare backbones by ROMP of norbornene
11 mL of toluene was added to each of the vials containing norbornene and capped. Toluene (1 mL) was added to each of the small vials containing catalyst and it was covered and shaken until the solution became a homogeneous green color.
Results and Discussion
- Macromonomers
- Polystyrene Bottlebrushes
- Deuterated Polystyrene Bottlebrushes
- Poly(tert-Butyl Acrylate) Bottlebrushes
- Polynorbornene Linear Polymers
- Poly Acrylic Acid Bottlebrushes by Hydrolysis of PtBA Bottlebrushes
The Nb of the resulting polymers (Table 2.5) increased monotonically with the M/C ratio, but deviated significantly. Due to the incompatibility with THF (mobile phase for GPC), it was not possible to determine the molecular weight and polydispersity of the PAA brushes.
Conclusions
Zhang, B., et al., Synthesis and solid-state structures of macromolecular cylindrical brushes with varying side chain length. Pesek, S.L., et al., Kleinhoek neutron scattering analysis of bottle brush polymers prepared via graft-by-polymerization. Zhang, M., et al., Amphiphilic cylindrical brushes with poly(acrylic acid) core and poly(n-butyl acrylate) shell and narrow length distribution.
Introduction
The shortest length scale is the approximate radius of the cross section of the flexible cylinder perpendicular to the contour of the spine. The use of the same polynorbornene backbones (almost identical Nb) as the polystyrene side-chain bottle brushes allowed the effect of side-chain chemistry to be observed. This provided insight into the effect of dramatic side chain conformational changes on the overall conformation of the bottlebrush.
Experimental
- Materials
- Multi Angle Laser Light Scattering with Gel Permeation Chromatography Multi Angle Laser Light Scattering (MALLS) was used in conjunction with Gel
- Dynamic Light Scattering
- Small Angle Neutron Scattering at NIST
- Small Angle Neutron Scattering at ORNL
The synthesis and characterization of the bottle brush polymer samples by MALLS/GPC is described in Chapter 2, and the sample characteristics are shown in Table 3.1. The constant C was chosen so that at q>0.3 Å-1 (where scattering is independent of structure and q) the residual intensity corresponds to the expected residual incoherent scattering due to the sample. The pH values of the aqueous brush solutions were tested and found to be lower than the original buffer solution due to the addition of a significant amount of acid.
Results and Discussion
Hydrodynamic and Gyration Radii of Bottlebrushes in Good Solvent Results
The ratio lk(Ns=65) to lk(Ns=25) is approximately the same for regular and deuterated polystyrene (1.8), which is lower than the ratio at. The scaling resulting from fitting the power law 𝑅𝑔 ~ 𝑁𝑏𝜈 to the local Rg(Nb) regions becomes smaller with increasing backbone length, as expected for a worm-like chain [16]. Hydrodynamic radii as a function of aspect ratio (length/radius) have been derived for extended spheroids [65] as well as for cylinders with aspect ratios between 4 and 40 [66, 67].
SANS of Unlabeled Bottlebrushes – Side-Chains in Good and Theta Solvents Results
All of the distribution patterns in Figure 3.5 have a two-plateau shape corresponding to the two-length scales of interest. This captured the shape of the distribution curve (the positions of the plateaus and the slopes of the curves) as well as the more complex patterns described in the literature[69]. The RCS appears to be independent of Nb, confirming the identification of the higher q length scale with the side chains.
SANS with Perdeuterated Side-Chains – The Backbone Conformation Results
We can therefore consider the RCS for the side chains as the undisturbed side chain dimensions. Qualitatively, the scattering curves I(q) for the bottlebrush backbone are remarkably similar to those of linear polynorbornene. In order to determine the side chain dimensions perpendicular to the backbone contour, SANS scattering patterns were taken for the same bottle brushes (dPS-25) in a.
Bottlebrushes with Poly(Acrylic Acid) Side Chains Results
The I(q) distribution curves for 140-PAA-95 and 730-PAA-95 show qualitatively similar characteristics to those of equivalent PtBA-95-based brushes. SANS patterns show a clear plateau at low q for both 140-PAA-95 and 730-PAA-95 at 0.1M salt concentrations and do not show a power-law dependence of I(q) ~ q-1 as expected for a fully elongated cylindrical object[54]. The only sample showing power law distribution at low q is 730-PAA-95 at pH 9 with 1.0M salt concentration.
Conclusions
Cheng, G., et al., Grafted polygon (norbornene) conformation of oligo(ethylene glycol) in solution: A small-angle neutron scattering study. Glinka, C., et al., The 30m Small Angle Neutron Scattering Instruments at the National Institute of Standards and Technology. Wignall, G.D., et al., The 40 m General Purpose Small Angle Neutron Scattering Instrument at Oak Ridge National Laboratory.
Introduction
When dissolved in a nematic small molecule LC, SGLCPs adopt anisotropic conformations: the orientation of the host pairs to that of the polymer's mesogens and, through the spacers, to the backbone segments [5–7] . The very weak molecular weight dependence of the scattering patterns led to the conclusion that these 5wt% solutions were in the semi-dilute regime. To go beyond previous studies, the present experiments are performed on matched pairs of side-by-side SGLCP homopolymers in the dilute regime to expose the overall size and shape of the polymer coil.
Experimental .1 Materials
- Synthesis of Perdeuterated 4-pentyl-4’-cyanobiphenyl (d-5CB)
- Characterization Methods
- Cell and Sample Preparation for SANS
- Precision Temperature Controlled Sample Environment
- Small Angle Neutron Scattering
The names of the polymers follow the general scheme of LC(repeat units)-PS(repeat units). . a.). Gel permeation chromatography was used to characterize the molecular weight and polydispersity of the SGLCPs. Both the magnetic field and the rubbed alignment layers of the cell were oriented horizontally with the pointer orientation lying parallel to it and perpendicular to the neutron beam.
Results
Homopolymer Conformation in Dilute Solution
In the current systems, the feature was observed in less than half of the samples; when present, it would often be associated with the nematic phase (the property will disappear on heating to the isotropic phase). Successful fits were obtained for all isotropic solutions and for the sector mean corresponding to the shorter axis of the ellipsoidal isointensity contours in the nematic phase, i.e. Ipar for CB and Iperp for BB. The small radii of both end-up and side-on polymers in the nematic phase are seen to be slightly smaller than their isotropic radii, which corresponds to the stretching of the polymer along the other axis.
SGLCP-b-PS Structure and Self-Assembly
Sector averages of the scattering patterns parallel and perpendicular to the nematic director (Figure 4.6) show the multiple length scales of anisotropy very clearly. Some of the objects seen in the colored images have lighter inner areas surrounded by a darker ring. This is consistent with the similarity in the q position of the rebounds seen in the sector averages Ipar(q) for the CB SGLCP-b-PS and Iperp(q) for its BB SGLCP-b-PS counterpart (Figure 4.6).
Discussion
- Mutually Orthogonal Anisotropic Structures at Different Length Scales
- Homopolymer Conformation in Dilute Solution
- SGLCP-b-PS Structural Length Scales
- Development of Toy Models to Test Plausibility of Interpretations for Scattering Patterns
To the best of our knowledge, the perpendicular orientation of the entire object with respect to the core has not been described in the literature. The primary physical properties expected of a core shell object are described in the following paragraphs. Scattering corresponding to the shorter axis of the corresponding SGLCP homopolymer (parallel to the end polymer router and perpendicular to the side polymer router) contains only one feature in the accessible region q; we extract the length scale associated with this feature using the Guinier function at low q and approximate the homopolymer-like scattering at high q using the Porod function (I(q) ~ q-n) [23].
Conclusions
Moussa, F., et al., Conformational anisotropy of liquid crystalline side-chain polymers: a small-angle neutron scattering study. Scruggs, N.R., et al., Self-assembly of wrapped/liquid-crystalline diblock copolymers in a liquid-crystalline solvent. Park, S.Y., et al., Self-assembly of dPS liquid crystalline diblock copolymer in a nematic liquid crystal solvent.
Introduction
Problematically, they were actually less effective in fog suppression than unmodified polybutadiene[17] due to the compact conformation of the supramolecules. The structure of the supramolecules formed in solution is critical to the performance of associating polymers as fog control agents. In the present study, we report the results of the first SANS study of pairwise complementary association of long telechelic polymers in hydrocarbon solvents.
Experimental .1 Materials
MALLS/GPC
Absolute polymer molecular weight[32] and polydispersity (PDI) were obtained using gel permeation chromatography with a Wyatt DAWN EOS multi-angle laser light scattering detector in series with a Waters 410 differential refractometer. Separation was achieved using four Agilent PLgel columns connected in series (pore size and 106 Å) with degassed THF at 0.9mL/min as the mobile phase.
Making Sample Solutions
Samples were prepared at a concentration of 5 mg/mL in THF and filtered through a 0.45μm PTFE membrane syringe filter immediately before injection. The vial was stirred overnight at 60 ℃ by immersing the vial in an oil bath on a magnetic stir/heat plate (IKA RCT). Mixed solutions of acid and base polymers were prepared by combining equal volumes of base polymer solutions and acid polymer solution in a new vial and then placing the mixture on a wrist-action shaker for at least 1 hour.
Small Angle Neutron Scattering at NIST and ORNL
Patterns for the three detector distances were combined using Igor PRO macros developed by Steve Kline [39] which were also used for subsequent processing and analysis. Data were analyzed using two scattering functions I(q): the polymer excluded volume function [40] used for polymers with non-Gaussian fractal scaling and the Beaucage function [41, 42] used for generalized fractal objects such as particles and aggregates. The Beaucage function is an empirical function that combines Guinier and Porod scattering[43] with the form.
Results
Solvent and Concentration Effects in Complementary Association
