This week, the ratings of four chemicals stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

PolyOne Corporation’s (POL) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. PolyOne is an international polymer services company with operations in North America, Europe, Asia, Australia, and South America. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Momentum and Sales Growth, POL also gets an F. Shares of the stock have been exchanging at an usually rapid pace, twice the rate of the week prior. The stock has a trailing PE Ratio of 45.30. To get an in-depth look at POL, get Portfolio Grader’s complete analysis of POL stock.

Marrone Bio Innovations, Inc.’s (MBII) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). The stock gets F’s in Earnings Momentum, Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of MBII stock.

The rating of Kraton Performance Polymers, Inc. (KRA) declines this week from a D to an F. Kraton Performance Polymers produces engineered polymers and styrenic block copolymers. The stock gets F’s in Earnings Momentum and Earnings Surprise. To get an in-depth look at KRA, get Portfolio Grader’s complete analysis of KRA stock.

Huntsman Corporation (HUN) earns a D this week, moving down from last week’s grade of C. Huntsman manufactures differentiated and commodity chemical products. The stock gets F’s in Earnings Momentum, Earnings Revisions and Earnings Surprise. For more information, get Portfolio Grader’s complete analysis of HUN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.