Synthesis and Properties of Copolymers of Diphenylsiloxane with Other Organosiloxanes

1989 ◽  
Vol 171 ◽  
Author(s):  
J. Ibemesi ◽  
N. Gvozdic ◽  
M. Kuemin ◽  
Y. Tarshiani ◽  
D. J. Meier

ABSTRACTWe describe the synthesis, characterization and properties of various types of siloxane polymers containing diphenylsiloxane (P) as a component. The polymer types include di-and tri-block copolymers with dimethylsiloxane (M) as the second component, and random and statistical copolymers with dimethylsiloxane or methylphenylsiloxane (P/M) as the second component. Such copolymers combine siloxane units whose polymers have very different properties. The polydiphenylsiloxane chain is rigid and inflexible, and the polymer is a highly crystalline solid with a liquid crystalline or condis crystalline state and a very high melting (clearing) temperature. In contrast, the polydimethylsiloxane or polymethylphenylsiloxane chains are very flexible and the polymers have very low glass transition temperatures.Polymers of controlled molecular composition, size and architecture were prepared by anionic polymerization of the ‘cyclic trimers’, using lithium-based initiators.The physical properties of the copolymers vary dramatically with composition and architecture. Two types of ‘random’ copolymers can be prepared. In one type, siloxane units of a given type are randomly placed in the chain in groups of three, i.e., the minimum sequence length of a given siloxane type is three siloxane units. In the other type of random copolymer, individual siloxane units are randomly distributed so that the minimum sequence length is a single siloxane unit. The properties of the two types are quite different, showing that subtle changes in sequence distribution can have major effects on physical properties. At molar ratios near 1/1 and with molecular weights of ∼105, the first type of ‘random’ copolymer is an elastic solid with appreciable mechanical properties, whereas the latter type is a sticky gum.Diblock copolymer (P-M) with dimethylsiloxane as the major component are paste-like, whereas the triblock (P-M-P) and star-block copolymers of the same composition are tough elastomers. The block copolymers are molecular composites, in which the polydiphenylsiloxane component separates into crystalline microphases with very uniform fibrillar or lamellar morphologies, and with widths or thicknesses comparable to the length of the polydiphenylsiloxane block, i.e, typically of the order of 100 Å.

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 627
Author(s):  
Marco Naddeo ◽  
Andrea Sorrentino ◽  
Daniela Pappalardo

Biodegradable block and random copolymers have attracted numerous research interests in different areas, due to their capability to provide a broad range of properties. In this paper, an efficient strategy has been reported for preparing biodegradable PCL-PLA copolymers with improved thermal, mechanical and rheological properties. Two block-copolymers are synthesized by sequential addition of the cyclic esters lactide (L-LA or D,L-LA) and ε-caprolactone (CL) in presence of a dimethyl(salicylaldiminato)aluminium compound. The random copolymer of L-LA and CL was synthetized by using the same catalyst. Chain structure, molar mass, thermal, rheological and mechanical properties are characterized by NMR, SEC, TGA, DSC, Rheometry and DMTA. Experimental results show that by changing the stereochemistry and monomer distribution of the copolymers it is possible to obtain a variety of properties. Promising shape-memory properties are also observed in the di-block copolymers characterized by the co-crystallization of CL and L-LA segments. These materials show great potential to substitute oil-based polymers for packaging, electronics, and medicine applications.


e-Polymers ◽  
2010 ◽  
Vol 10 (1) ◽  
Author(s):  
Zeynep Özyürek ◽  
Brigitte Voit ◽  
Franziska Krahl ◽  
Karl-Friedrich Arndt

AbstractBlock and random copolymers containing N-isopropylacrylamide and (α- D-glucofuranosyl)-6-methacrylamido units were analyzed according to their temperature dependent aggregation behavior. Whereas a 45:55 random copolymer does not exhibit any LCST behavior below 100 °C due to the incorporation of the hydrophilic glyco monomer units, the phase transition could be retained in the physiological range in block copolymers even at a glyco monomer content above 55 mol%. DSL studies revealed that the aggregates of about 50 nm are stabilized above the transition temperature when the glyco monomer block dominates, whereas a glyco block molar ratio of 45% is not sufficient to prevent precipitation of the polymers as evidenced by turbidity measurements. Temperature dependent DLS studies revealed further that below the phase transition temperature an equilibrium between single macromolecules and aggregates is formed.


Author(s):  
Afzana Anwer ◽  
S. Eilidh Bedford ◽  
Richard J. Spontak ◽  
Alan H. Windle

Random copolyesters composed of wholly aromatic monomers such as p-oxybenzoate (B) and 2,6-oxynaphthoate (N) are known to exhibit liquid crystalline characteristics at elevated temperatures and over a broad composition range. Previous studies employing techniques such as X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) have conclusively proven that these thermotropic copolymers can possess a significant crystalline fraction, depending on molecular characteristics and processing history, despite the fact that the copolymer chains possess random intramolecular sequencing. Consequently, the nature of the crystalline structure that develops when these materials are processed in their mesophases and subsequently annealed has recently received considerable attention. A model that has been consistent with all experimental observations involves the Non-Periodic Layer (NPL) crystallite, which occurs when identical monomer sequences enter into register between adjacent chains. The objective of this work is to employ electron microscopy to identify and characterize these crystallites.


2013 ◽  
Vol 652-654 ◽  
pp. 459-462
Author(s):  
Ya Tong Guo ◽  
Zhu Zheng ◽  
Zhen Qi Hou ◽  
Jie Du

A series of biodegradable segmented liquid crystalline poly(ester-urethane)s were prepared by solution polymerization of poly(L-lactic acid) (PLLA), mesogenic diol prepolymer poly(butylene terephthaloyldioxy dibenzoates) (MD), and hexamethylene diisocyanate (HDI). The MD content was varied from 0 to 40 mol% so that the effects of the mesogen content on the thermal and physical properties, and hydrolytic degradation were examined respectively. It was found that introducing mesogens units could increase the thermal stability and the elastic properties, while reduced the phase transition temperatures and the hydrolytic degradation rate.


2010 ◽  
Vol 144 ◽  
pp. 143-157 ◽  
Author(s):  
Federica Lo Verso ◽  
Athanassios Z. Panagiotopoulos ◽  
Christos N. Likos

2014 ◽  
Vol 47 (12) ◽  
pp. 4048-4055 ◽  
Author(s):  
Jose Alonzo ◽  
Juan Pablo Hinestrosa ◽  
Jimmy W. Mays ◽  
S. Michael Kilbey

Sign in / Sign up

Export Citation Format

Share Document