Narrow molecular weight

Most of the LFRP research ia the 1990s is focused on the use of nitroxides as the stable free radical. The main problems associated with nitroxide-mediated styrene polymerizations are slow polymerization rate and the iaability to make high molecular weight narrow-polydispersity PS. This iaability is likely to be the result of side reactions of the living end lea ding to termination rather than propagation (183). The polymerization rate can be accelerated by the addition of acids to the process (184). The mechanism of the accelerative effect of the acid is not certain. 

Low molecular weight, narrow MWD polymer—used widely for injection moulding and rotational moulding. 

Anionic polymerization in suitable systems allows the preparation of polymers with controlled molecular weight, narrow molecular weight distributions and functional termination. The functional termination of a living anionic polymerization with a polymerizable group has been used frequently in the preparation of macromonomers (4). Our research has encompassed the anionic homo and block copolymerizations of D- or hexamethyl cyclotrisiloxane with organolithiums to prepare well defined polymers. As early as 1962 PSX macromonomers were reported in the literature by Greber (5) but the copolymerization of these macromonomers did not become accepted technique until their value was demonstrated by Milkovich and... 

Me) was R = Me > Bu > Pr-opposite to that observed for the heterogeneous system. In addition, the supported catalysts produced polyethylene with higher molecular weights, narrower molecular weight distributions and higher bulk densities than that produced by the homogeneous systems. 

However, the ROP of lactide and glycolide remains by far the most extensively practiced method in industry and academia for the preparation of polyesters. This method allows a better control of polymerization in terms of high molecular weight, narrow polydispersity, monomer-to-initiator ratio and sequence, well-defined... 

Our group described a simple access to well-defined hyperbranched polyamines from hyperbranched PEI with different molecular weights, narrow molecular weight distributions, and an adjustable degree of branching [91]. According to this protocol fully branched analogs of polypropyleneimine (PPI) and polyamidoa-mine (PAMAM) dendrimers can be derived from hyperbranched PEI (Mw = 5,000, and 25,000 g mol-1) in a two-step synthetic process (Scheme 2). 

Schriemer D, Li L (1996) Detection of high molecular weight narrow polydisperse polymers up to 1.5 million daltons by MALDI mass spectrometry. Anal Chem 68 2721-2725... 

An increase in molecular weight leads to significant improvements in the fatigue life of both amorphous and crystalline polymers. This improvement is attributed primarily to an increase in craze stability and to an improvement in the fibril density, contributing to greater resistance to liquid transport. As the fraction of low-molecular-weight molecules cannot contribute to ESCR, it is found that for similar molecular weights narrow MWDs are clearly superior. 

According to the MC simulation, the high molecular weight, narrow distribution component consists of the largest polymer molecule in each polymer particle, and the bimodal MWD is formed because of the limited space effects. 

Anionic polymerization, however, can be used to produce high molecular weight narrow distribution polystyrene. If all the chains are initiated at the same time and the temperature is kept low to minimize chain transfer, molecular weight distributions very close to monodisperse can be produced. The commercial uses of these polymers seem to be limited to instrument calibrations and laboratory studies of the effects of molecular weight on rheology and physical properties. However, anionic polymerization as a potential commercial method for producing polystyrene has been extensively studied by Dow and others. The potential for high polymerization rates, complete conversion of... 

Anionicallv Polymerized A-B-A Model Polymers Predictable Molecular Weights Narrow Molecular Weight Distributions High-Purity Block Compositions Facile Coupling or End-Group Functionalization... 

The development of controlled radical polymerization (CRP) methods,(1,2) including atom transfer radical polymerization (ATRP),(3-6) nitroxide-mediated radical polymerization,(7) and reversible addition fragmentation chain transfer polymerization,(8,9) has led to the synthesis of an unprecedented number of novel, previously inaccessible polymeric materials. Well-defined polymers, i.e., polymers with predetermined molecular weight, narrow molecular weight distribution, and high degree of chain end functionalization, prepared by... 

SBR involves the use of alkyllithium catalysts. Solution SBR generally has a higher molecular weight, narrower molecular weight distribution, and higher cw-diene content than emulsion SBR. 

High molecular weight narrow molecular weight distribution increases cohesive bond strength... 

CRP provides a versatile route for the preparation of (co) polymers with controlled molecular weight, narrow molecular weight distribution (i.e., Mw/Mn, or PDI < 1.5), designed architectures, and useful end-functionalities. Various methods for CRP have been developed however, the most successful techniques include ATRP, stable free radical polymerization, " and reversible addition fragmentation chain transfer (RAFT) polymerization. " " CRP techniques have been explored for the synthesis of gels " " and cross-linked nanoparticles of well-controlled polymers in the presence of cross-linkers. 

Schriemer, D. C. and Li, L., Detection of High Molecular Weight Narrow Poly-disperse Polymers up to 1.5 Milion Daltons by MALDI Mass Spectrometry, Anal. Chem., 68, 2721, 1996. 

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