Chain architecture branching

The bulk properties of PLA are greatly affected by the molecular weight of the polymer, the chain architecture (branched vs. linear), and the degree of crystallinity in the polymer (21,22). The acheivable crystallinity of PLA is determined by the relative proportions of L- and D-lactide in th6 polymer backbone the greater the optical purity, the higher the crystallinity. 

Figure C2.1.2. Polymers witli linear and nonlinear chain architectures. The nonlinear polymers can have branched chains. Short chains of oligomers can be grafted to tire main chain. The chains may fonn a. stor-like stmcture. The chains can be cross-linked and fonn a network.

The chain architecture and chemical structure could be modified by SCVCP leading to a facile, one-pot synthesis of surface-grafted branched polymers. The copolymerization gave an intermediate surface topography and film thickness between the polymer protrusions obtained from SCVP of an AB inimer and the polymer brushes obtained by ATRP of a conventional monomer. The difference in the Br content at the surface between hyperbranched, branched, and linear polymers was confirmed by XPS, suggesting the feasibility to control the surface chemical functionality. The principal result of the works is a demonstration of utility of the surface-initiated SCVP via ATRP to prepare surface-grafted hyperbranched and branched polymers with characteristic architecture and topography. 

At the same time, the macromolecules might be classified according to whether their chains have only one kind of atoms - like carbon - in the backbone (isochains) or different elements (heterochains). Concerning their chain architecture, polymers are subdivided into linear, branched, comb-like, crosslinked, dendritic, or star-like systems. 

As a result of the branched chain architecture, TASP molecules exhibit some unique conformational properties)5 12-14 47 75 76 148 For example, the folding to a compact state proceeds via two distinct steps the onset of secondary structure in the attached peptide blocks followed by their template-directed self-assembly to a three-dimensional packing topology. Due to its characteristic branched chain connectivity, the conformational space accessible in the unfolded state is considerably reduced compared to a linear chain of similar size (excluded volume effect), resulting in a smaller chain entropy. Thus, folded TASP molecules are expected to show higher thermodynamic stability compared to unbranched polypeptides of comparable size. 

There are several kinds of polyethylene (LDPE, LLDPE, HDPE, UHMWPE), which are synthesized with different molecular weights and chain architectures. LDPE and LLDPE refer to low-density polyethylene and linear low-density polyethylene, respectively. These polyethylenes generally have branched and linear chain architectures, respectively, each with a molecular weight of typically less than 50,000 g/mol. 

Figure 1.11 Polyethylene chain architectures, (a) Linear, almost no branches, (b) Linear varying amount of short branches and (c) Branched with a large amount of short branches.

Polyethylenes include HOPE, LLDPE and LDPE. The main difference among these polymers is their chain architecture (Figure 1.11). HDPE is a linear polymer with almost no branches, LLDPE is a linear polymer with a varying amount of short branches, and LDPE is a branched polymer (0.5-3 long branches per 1000 carbons in the backbone) with a large amount of short branches (30 short branches per 1000 carbons in the backbone) [24]. 

Broadband dielectric spectroscopy (BDS) is a versatile experimental tool to study the dynamics of polymeric systems. In its modem form it covers the extraordinary frequency range from 10 Hz to 10 Hz with the option to extend both limits to lower and higher values, respectively. This enables one to analyse the molecular d3mamics on a large time scale especially if the temperature of the sample is varied as well. In the present review article examples will be discussed for polymers of widely varying molecular architectures (linear and cyclic chains, star-branched systems, and liquid crystalline polymers). 

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